Operating type

Openable – hinged or projected

Hinged or projected products generally have lower air leakage rates, because the sash closes by pressing against the frame and so compression-type weather-stripping can be used. They provide excellent ventilation potential because the open sash, protruding from the plane of the wall, can be used to catch breezes. They tend to have a higher frame fraction to be strong enough to withstand wind forces.

Openable – sliding

Sliding products generally have higher air leakage rates, because the weather-stripping must still allow the sash to slide past. They provide lower ventilation potential because the opening is in the plane of the wall, and the opening area cannot be more than half of the glass area. They tend to have a lower frame fraction because the sash is supported on two sides by the frame, however this means they will have a higher SHGC.

Non-openable – fixed

Fixed products generally have lower air leakage rates. They provide no ventilation potential. They tend to have a lower frame fraction because the sash is supported on two sides by the frame.

These characteristics are summarised in the table below.

Operating type

Ventilation potential

Air infiltration

Frame fraction

Hinged / projected

high

medium

high

Sliding

medium

high

medium

Fixed

none

low

low

Frame material

Aluminium frames are very common, but tend to have higher U-values because aluminium conducts heat readily.

Thermally broken aluminium frames improve on the performance of a standard aluminium frame by separating the interior and exterior parts of the frame with a less conductive material joining them. These are not to be confused with "thermally improved" frames.

uPVC (un-plasticised polyvinyl chloride) frames are made from rigid PVC, and have similar thermal performance to timber frames.

Fibreglass frames are made from glass-reinforced polyester, and have similar thermal performance to timber frames.

Composite frames use a durable material on the exterior section (such as aluminium or uPVC) and a decorative material on the interior section (such as timber).

Glazing system type

Single-glazing will generally have a higher U-value than double-glazing.

Double-glazing with air fill has two layers of glass with an airspace in between. The U-value will generally be lower than single-glazing.

Double-glazing with argon fill offers an improvement of between 5% and 20% over double-glazing with air fill.

Outer glass type

Clear glass will admit a large part of the light and heat.

Tinted/toned glass admits less of the light and heat by absorbing it. Spectrally selective tints are also available that preferentially transmit more of the light and absorb more of the heat (in the near-infrared spectrum).

Hi Tsol Low-e (pyrolytic or hard-coat Low-e) coatings reduce the emissivity of a surface of the glass so that heat is preferentially emitted in the opposite direction.

Lo Tsol Low-e (soft-coat Low-e) coatings not only reduce the emissivity of a surface of the glass, but are spectrally selective to preferentially transmit more of the light and less of the heat (in the near-infrared spectrum).

Certifying the windows and glazed doors in your dwelling

For the following glass and frame types, you are not required to provide certification of the U-value and SHGC of the windows installed in your dwelling:

Descriptions on the BASIX certificate for the above glass and frame types must match the windows installed in your dwelling.

For all other frame and glass types

The BASIX certificate shows the maximum allowable U-value and acceptable SHGC range for the frame and glass types that you have selected. The acceptable SHGC range is +/- 10% of the value from the 88 default windows recognised in the BASIX DIY method.

Description of frame and glass types are included in the BASIX certificate as a reminder of the types you selected. It is not mandatory to match the descriptions and matching them is not sufficient on its own for certification. For these types, you must provide certification of the U-value and SHGC under National Fenestration Rating Council (NFRC) conditions.

Frame and glass type not on the list

You can still use another system if you know its U-value and SHGC even if the description does not match. Select from the 88 default windows that have a U-value higher than your type. The SHGC of your type should fall within 10% of the SHGC of the type that you select, or within the acceptable SHGC range on the BASIX certificate.

If you have steel-framed windows, select aluminium frame with the appropriate glass and operating type.

If you have single-sheet obscure glass, select 'single glazed tinted' glass with the appropriate frame and operating type.

If you are using glass bricks, select double-glazed clear (air-filled) glass with aluminium frame that is non-openable or fixed.